The present invention relates to a method of discharging intermittently liquid and a plunger pump suitable for a high pressure liquid injecting apparatus and more particularly, such a method and pump capable of increasing discharge pressure of the liquid upon its intermittent discharge. International publication of international application WO 91/07077 discloses intermittently injecting liquid under pressure through nozzles into the turf to form aerating holes in the turf. The high pressure liquid injecting apparatus includes an accumulator for accumulating liquid discharged from a pump and an intermittent valve connected between the accumulator and the nozzles to intermittently inject the liquid under pressure through the nozzles.
The high pressure liquid injecting apparatus disclosed in international application WO91/07077 is complicated in structure because of the need for the accumulator and the intermittent valve. Since the accumulator and the intermittent valve have no chemical and wear resistances, there might cause difficulties in injecting liquid of chemicals, fertilizer or the like containing fine particles for extermination and fertilization as well as aerating holes.
Japanese Patent Application Heisei 5-67342 discloses utilizing intermittent discharge of liquid from a plunger pump to intermittently inject the liquid through nozzles. This has an advantage in that any need for the accumulator and the intermittent valve as described can be eliminated. In the conventional plunger pump, the plunger is connected through a connecting rod to a crank shaft and rotation of the crank shaft causes the plunger to be reciprocated at a speed of displacement following a sine curve. Thus, an angle of rotation of a crank shaft at the discharge stroke is 180.degree. . In order to increase the discharge pressure of liquid upon its intermittent discharge, increase in a speed of an engine is required to increase the speed of rotation of the crank shaft of the pump.